Python LazyDict
Filed under Python on nov 04, 2008
I’m a great fan of the dot notation, instead of foo['bar'] hash notation. Also because the Django and Jinja templating engines use dot notation for all their object attribute/key lookups.
You can also use assignments and lookups on a dictionary, using the __setattr__ and __getattr__ methods:
class LazyDict(dict):
def __getattr__(self, attr):
if attr in self:
return self[attr]
else:
raise AttributeError, "'%s' object has no attribute '%s'" \
% (self.__class__.__name__, attr)
def __setattr__(self, attr, value):
if hasattr(super(LazyDict, self), attr):
raise AttributeError, "'%s' object already has attribute '%s'" \
% (self.__class__.__name__, attr)
self[attr] = value
This allows you to do:
>>> from lazydict import LazyDict >>> foo = LazyDict() >>> foo.bar = 42 >>> foo.bar 42 >>> foo.biz = LazyDict() >>> foo.biz.qux Traceback (most recent call last): File "<stdin>", line 1, in <module> File "lazydict.py", line 6, in __getattr__ AttributeError: LazyDict instance has no attribute 'qux' >>> foo.biz.qux = object() >>> foo.biz.qux <object object at 0xb7d26468>
Update Nov 12, 1008
Incorporated Floes’ suggestions from the comment below, thanks!
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